1. Field of the Invention
The present invention relates to a linear motion guiding apparatus for a heavy load, in which rollers and balls are used as rolling members in combination.
2. Description of the Related Art
With respect to a conventional linear motion guiding apparatus for a heavy load, there is known a linear roller guiding apparatus, in which a plurality of trains of rolling members are composed only of rollers 101 as shown in example in FIG. 5(a).
More specifically, in such a linear roller guiding apparatus, a movable block 103 is movably guided along a guide rail 102 through the rollers 101, 101, 101, 101, which are arranged to form two trains of rollers on each of the right and left-hand side surfaces of the guide rail 102 so as to provide the total number of trains of four.
Such a full-roller type linear motion guiding apparatus however has problems that a pre-load applied to the rollers 101, an inverse radial load (a lifting load) having a function of pulling the movable block 103 apart from the upper surface of the guide rail 102 and a transverse load having a function of shifting horizontally the movable block 103 relative to the guide rail 102 may easily cause the right and left-hand wing members 104, 104 of the movable block 103 to be deformed outward so as to be apart from each other under the function of the moment. Such deformation of the wing members 104, 104 makes it impossible to maintain a proper parallelism of the roller running surface 105 of the guide rail 102 and the roller running counter-surface 106 of the movable block 103, between which the rollers are held, as illustrated with exaggeration in FIG. 5(b). Accordingly, a proper linear contact of the roller 101 with these surfaces 105, 106 cannot be maintained with the result that a load concentration may occur on the roller end 101a, thus decreasing the load capacity as well as durability, and making it impossible to bring the ability of the roller 101 into full play.
When a pre-load is applied for example to the roller 101 as shown in FIG. 5(c), the inner surfaces of the both wing members 104 of the movable block 103 are urged by a reaction force Fi of the pre-load of the roller 101, and the moment Mi having the function of expanding the wing members 104, 104 is generated, thus resulting in deformation of the wing members 104, 104.
The inverse radial load Fu is applied to the movable block 103 through a bolt 108 by means of which a member 107 to be guided is fixed to the movable block 103, as shown in FIG. 5(d). The lower rollers 101 arranged on the right and left-hand sides of the guide rail 102 carry the above-mentioned load Fu. Since the bolt 108 to which the load is applied is however apart from the roller 101 in the horizontal direction, the inverse radial load Fu and the reaction force Nu of the contact portion of the roller 101 form a couple of forces, resulting in occurrence of the moment Mu having the function of expanding the wing members 104, 104 so as to cause deformation of the wing members 104, 104.
The transverse load F.sub.T is applied to the movable block 103 through the bolt 108 as shown in FIG. 5(e). The two trains of rollers 101 arranged on the one wing member 104 carries the above-mentioned load F.sub.T. Since the bolt 108 to which the load is applied is however apart from the roller 101 in the vertical direction, the moment M.sub.T having the function of expanding the one wing member 104 so as to cause deformation of the wing member 104.